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Abdomen:Venous:Portal system
Portal vein (PV) is the main vessel in the portal venous system and drains blood from the gastrointestinal tract and spleen to the liver. The portal vein, usually measures approximately 8 cm in adults Origin: behind the neck of the pancreas and is usually formed by the confluence of the superior mesenteric and splenic veins Course: * It runs vertically upwards in the free edge of the lesser omentum, lying behind the bile duct and hepatic artery. * Immediately before reaching the liver, the portal vein divides into left portal vein (supplying liver segments II, III, IV) and the right portal vein. * This subsequently divides further into anterior (supplying liver segments V and VIII) and posterior (supplying liver segments VI and VII) portal veins . * Left branch receives ligamentum teres - obliterated umbilical vein. * It ramifies further, forming smaller venous branches and ultimately portal venules. Relations: * Posterior: IVC * Anterior: pancreas and D1 of duodenum. Each portal venule courses alongside a hepatic arteriole and the two vessels form the vascular components of the portal triad. These vessels ultimately empty into the hepatic sinusoids to supply blood to the liver. 75% of the blood supplied to the liver comes from the portal vein, but it only supplies 50% of the oxygen supply to the liver. Variant anatomy The overall incidence of portal vein variation is reported to be 25-30%. There is an increased risk of bile duct hilar anatomical variation in the presence of portal vein variants. These anatomical variants should be recognized prior to procedures such as liver transplantation, complex hepatectomy and portal vein embolisation. Portal vein trifurcation: this is the most common variant. The portal vein divides into three branches; the left portal vein, the right anterior portal vein, the right posterior portal vein. Right posterior portal vein splits off as the first branch of the portal vein. The right anterior and the left portal veins then originate from a common trunk. Tributaries: * Lower third of oesophagus drain into oesophageal veins, to the left gatric vein. Upper third drain into the azygos vein. The left gastric, pass along the lesser curvature, in the posterior wall to join the portal vein. * Right gastric run along lesser curvature to the pylorus and enter the portal vein. * Short gastric and left gastroepiploic vein run with arteries to the hilum and spleen and empty into the splenic vein. The splenic vein travel with the tail of the pancreas below the splenic artery, in the splenorenal ligament and continues to the right, posterior to the body of the pancreas, lying on the hilum of kidney, left psoas muscle, left sympathetic trunk, left crus of the diaphragm, aorta, SMA, and IVC to terminate in the portal vein. At the left crus it receives the inferior mesenteric vein. * The right gastroepiploic vein join the SMV at the lower border of the neck of the pancreas. * Cystic vein join the right branch of the portal vein. * Paraumbilical veins running with the ligamentum teres join the left branch.